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Engineered Hens Produce Human Proteins in Eggs

Genetically-modified chickens

Genetically-modified chickens produce human therapeutic proteins (Norrie Russell, Roslin Institute)

28 Jan. 2019. An animal biology lab in Scotland developed genetically engineered chickens that efficiently produce human therapeutic proteins in their eggs. A team from the Roslin Institute at University of Edinburgh in the U.K. describes its process in a recent issue of the journal BMC Biotechnology, and began commercializing the technology through a spin-off enterprise.

Researchers from the Roslin Institute that studies animal health, but also applies its findings to controlling human diseases, are seeking more productive and less expensive methods for producing biologic drugs such as engineered human proteins, with animal physiology. These engineered proteins, such as enzymes and cytokines, treat a number of diseases, including cancer, but are typically made in mammalian cell cultures, which the authors say are costly, produce low volumes, and require a lot of purification.

The Roslin team, led by veterinary geneticist Helen Sang, proposes new methods with genetically engineered animals to produce synthetic human proteins. Using large livestock species, such as engineered cattle and sheep to produce milk with human proteins, is being studied and advanced, as reported by Science & Enterprise in August 2018. Livestock, however, require a lot of room and feed to raise, have few offspring, and a long gestation time, thus the need for more efficient and less costly methods. Separating purified proteins from the milk is also tricky, and there’s a high risk the human proteins can damage cells and tissue in the animals.

The researchers instead genetically engineered chickens, with eggs from hens employed as bioreactors to produce human therapeutic proteins. Hens can lay more than 300 eggs per year, with the whites in each egg producing nearly 3.5 grams of protein, thus a typical biologic drug dose could be produced with only 3 eggs. Chickens are also less expensive to raise than livestock. In addition, chickens have internal protein synthesis processes in their cells similar to humans, which improves the likelihood of producing useful proteins and reduces the chance for invoking an immune reaction.

To prove the concept, Sang and colleagues engineered chickens with gene transfers using benign lentiviruses to deliver human genes coding for 2 types of therapeutic proteins. The first protein generated is interferon-alpha-2a, an engineered biologic in use since the 1980s for treating viral diseases and some types of leukemia. The team retrieved 15 milligrams of interferon-alpha-2a from 100 milliliters of egg white from the engineered hens. In lab cultures, the interferon-alpha-2a produced by the eggs demonstrates antiviral activity against H1N1 flu viruses.

The researchers then produced a newer type of biologic protein, known as colony stimulating factor, or CSF1, that supports macrophages, a type of white blood cell in the immune system. The team engineered a class of CSF1 called fragment crystallizable, or FC cytokine that fuses with immunoglobulin G antibodies, now being developed for regenerative medicine. Using eggs laid by engineered hens, the researchers produced CSF1 for pigs and humans that in lab tests interacts with mouse bone marrow. In the case of CSF1 for pigs, tests in lab mice induced with liver and spleen damage show the engineered CSF1 generates macrophages which help repair the damage, as shown in increased liver and spleen weights in the test mice.

In addition, the team froze the egg whites with engineered proteins, which remained active when thawed a month later. This ability to freeze and store engineered proteins in egg whites adds to the market value of the discovery. Roslin Technologies, a spin-off company from Roslin Institute is commercializing the now-patented process.

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